Some printing systems have a reservoir to store printing fluid, such as ink, and a supply system to supply the printing fluid from the reservoir to a printhead, to enable the printhead to apply the printing fluid to a substrate to form an image on the substrate during a printing operation. In some printing systems, the supply system comprises additional storage, intermediate the reservoir and the printhead. The additional storage may provide a buffer of printing fluid to enable the reservoir to be refilled or changed during a printing operation.